Cloud with volumes renders blurry
Two things that jumped out to me.
First, the noise texture has a Detail slider.  This increases computation somewhat.

The second thing is messing with the settings in Render Properties -&gt; Volumes.  Try decreasing the Viewport and Render Step Rate and possibly increase the number of Max Steps.
This may not be necessary depending on your scene, I think it mostly helps with large volume objects but clouds are typically pretty large.  This will unfortunately make volumes take a long time to render.  That's the cost of accuracy.

Just for reference, even on this default cube sized volume you can see we run into some strange effects on the top boundary with the default volume settings.  These images were both 512 samples in Cycles, no denoising.